Hi Yanleeau,

You are right - there is very little information about COT
grafting - I've looked, too. Here is the little bit I have found.

I have found this verbiage on numerous websites, so I'm not
sure who to credit:

Euphorbia milii can be propagated by V-grafting. This method is often used to lower the risk
of rot associated with direct rooting of cuttings. The extra skill required for grafting means
this technique is more likely to be used for select cultivars by growers and
serious hobbyists.

A stock plant is cut at two-to-three inches above the soil
line. A 3/4-inch, deep, V-shaped cut is
made into the stock.

A two-to-three inch stem tip (scion) is removed from the
plant to be propagated, and the cut end is trimmed to form a 3/4-inch wedge,
matching the V-cut in the stock.

Immediately after the cut surfaces stop bleeding, insert the
scion into the stock, and wrap them together securely with grafting tape. Cover the whole pot with a clear plastic bag
for about two weeks.

The web page at the link below has some photos, although
they are small. Note that this graft is
done using the V-cut technique. Also
note that in the last photo, it is difficult to see, but the grower is sliding
a plastic bag over the plant. (This web
page also references a "video clip", but I have been unable to find
it.):

Tropica Nursery - Grafting

The YouTube video linked below shows grafting of Euphorbia
turbiniformis but it provides two important points that may also be applicable
to E. milii. (Skip forward to the 5:43
mark if you want to get right to the cutting and grafting.) First, use a spray bottle with distilled
water to stop the latex "bleeding" and to enable the wound to dry
faster. The grower applies a water spray
after every cut. Second, apply constant
pressure at the graft to remove any water or latex between the two
surfaces. He does it with rubber
bands. So it might not be enough to just
tie them together - you may have to find a way to apply pressure at the
union. I'm thinking very small,
light-weight rubber bands, hooked to the thorns, may be helpful (?).

YouTube: Grafting of Euphorbia

Are you a "serious hobbyist"? If you give it a try, please post some photos
and keep us updated!

Carol in Jacksonville